Things You'll Need
Instructions
Purchase a third-party flash cart that allows the user to import files to the DSi. Examples of such devices include the R4 DSi and the DSTT. You will also need to obtain a MicroSD card if your device does not come with one.
Download and install Moonshell to your computer, an add-on for your DSi that allows video playback.
Download and install a DPG converter. These programs convert videos from various formats to DPG, a format that your DSi can read. Examples include BatchDPG, 4Media DPG Converter, and Aiseesoft DPG Converter.
Import your video files to your DPG converter of choice and export to DPG. For example, in BatchDPG, click "Browse" to find your file and click "Run" to start the conversion.
Plug your MicroSD card into your computer. Copy the converted files as well as the Moonshell install files to your card.
Insert your R4 or DSTT into your DSi and insert your MicroSD into the device's card slot.
Start your DSi and select "_MOONSHL.NDS" from the list of files. Press "A" to start the installation.
Select the "Moonshell" icon on your DSi main menu once installed. Select your desired file from the menu to start playing your video.